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    • 5. 发明授权
    • Magnetic resonance imaging of short T.sub.2 species with improved
contrast
    • 短T2物种的磁共振成像具有改善的对比度
    • US5150053A
    • 1992-09-22
    • US645859
    • 1991-01-25
    • John M. PaulySteven M. ConollyDwight G. Nishimura
    • John M. PaulySteven M. ConollyDwight G. Nishimura
    • A61B5/055G01R33/48G01R33/50G01R33/56G01R33/561
    • G01R33/446G01R33/50G01R33/56
    • Magnetic resonance signals for imaging species having short spin-spin relaxation times (T.sub.2) are obtained without the need for a refocusing lobe. A series of RF excitation pulses are applied to the species with magnetic resonance signals being detected after each RF excitation pulse is applied. The magnetic resonance signals are then combined to provide the imaging signals. In one embodiment, each RF excitation pulse is half of a conventional slice-selective pulse with each pulse being slewed to zero. Contrast between the imaged short T.sub.2 species and longer T.sub.2 species can be enhanced by first applying an RF signal having sufficient amplitude to excite the longer T.sub.2 species but insufficient amplitude to excite the short T.sub.2 species whereby the longer T.sub.2 species are tipped by the RF signal. A magnetic gradient can then be applied to dephase the tipped nuclei of the longer T.sub.2 species. The imaging signals are then obtained from magnetic resonance signals from the short T.sub.2 species.
    • 获得具有短自旋 - 自旋弛豫时间(T2)的成像物质的磁共振信号,而不需要重新聚焦波瓣。 在施加每个RF激励脉冲之后,对具有磁共振信号的物种施加一系列RF激励脉冲。 然后将磁共振信号组合以提供成像信号。 在一个实施例中,每个RF激励脉冲是常规切片选择脉冲的一半,其中每个脉冲被转换为零。 可以通过首先施加具有足够振幅的RF信号来激发较长的T2物种但不足的幅度来激发短的T2物种,从而通过RF信号使更长的T2物种倾斜,可以增强成像的短T2物种与较长的T2物种之间的对比。 然后可以应用磁梯度来去除较长T2物种的尖端核。 然后从来自短T2物种的磁共振信号获得成像信号。
    • 7. 发明授权
    • Catalyzing the transient response in steady-state MRI sequences
    • 在稳态MRI序列中催化瞬时反应
    • US06452387B1
    • 2002-09-17
    • US09801424
    • 2001-03-07
    • Brain A. HargreavesShreyas VasanawalaJohn M. PaulyDwight G. Nishimura
    • Brain A. HargreavesShreyas VasanawalaJohn M. PaulyDwight G. Nishimura
    • G01V300
    • G01R33/5613
    • A steady-state condition for tipped nuclear spins is accelerated or catalyzed by first determining magnetization magnitude of the steady state and the scaling magnetization along one axis (Mz) to at least approximate the determined magnetization magnitude. Then the scaled magnetization is rotated to coincide with a real-valued eigenvector extension of the tipped steady-state magnetization. Any error vector will then decay to the steady-state condition without oscillation. In one embodiment, the magnetic resonance imaging utilizes steady-state free precession (SSFP). The scaling and rotating steps are followed by the steps of applying read-out magnetic gradients and detecting magnetic resonance signals from the tipped nuclear spins. The magnetization magnitude is determined by eigenvector analysis, and the eigenvector extension is a real-valued eigenvector determined in the analysis.
    • 通过首先确定稳态的磁化强度和沿着一个轴(Mz)的缩放磁化强度至少接近确定的磁化强度,来加速或催化尖端核自旋的稳态条件。 然后,缩放的磁化被旋转以与尖端稳态磁化的实数特征向量延伸一致。 任何误差矢量都会衰减到稳态,而不会产生振荡。 在一个实施例中,磁共振成像利用稳态自由进动(SSFP)。 缩放和旋转步骤之后是应用读出磁梯度并从尖端核自旋检测磁共振信号的步骤。 磁化强度由特征向量分析确定,特征向量扩展是在分析中确定的实值特征向量。
    • 8. 发明授权
    • Linear combination steady-state free precession MRI
    • 线性组合稳态自由进动MRI
    • US06307368B1
    • 2001-10-23
    • US09312025
    • 1999-05-14
    • Shreyas S. VasanawalaJohn M. PaulyDwight G. Nishimura
    • Shreyas S. VasanawalaJohn M. PaulyDwight G. Nishimura
    • G01V300
    • G01R33/5613G01R33/446
    • A fast, spectrally-selective steady-state free precession (SSFP) imaging method is presented. Combining k-space data from SSFP sequences with certain phase schedules of radiofrequency excitation pulses permits manipulation of the spectral selectivity of the image. For example, lipid and water can be rapidly resolved. The contrast of each image depends on both T1 and T2, and the relative contribution of the two relaxation mechanisms to image contrast can be controlled by adjusting the flip angle. Several applications of the technique are presented, including fast musculoskeletal imaging, brain imaging, and angiography. The technique is referred to herein as linear combination steady-state free precession (LCSSFP) and fluctuating equilibrium magnetic resonance (FEMR).
    • 提出了一种快速,频谱选择性的稳态自由进动(SSFP)成像方法。 将来自SSFP序列的k空间数据与射频激发脉冲的某些相位调度组合允许操纵图像的光谱选择性。 例如,脂质和水可以快速解决。 每个图像的对比度取决于T1和T2,并且可以通过调整翻转角度来控制两个松弛机制对图像对比度的相对贡献。 提出了该技术的几个应用,包括快速肌肉骨骼成像,脑成像和血管造影。 该技术在此被称为线性组合稳态自由进动(LCSSFP)和波动平衡磁共振(FEMR)。
    • 9. 发明授权
    • Diminishing variance process for real-time reduction of motion artifacts
in MRI
    • 减少MRI中运动伪像的实时方差过程
    • US5427101A
    • 1995-06-27
    • US286049
    • 1994-08-04
    • Todd S. SachsCraig H. MeyerDwight G. Nishimura
    • Todd S. SachsCraig H. MeyerDwight G. Nishimura
    • G01R33/56G01R33/567A61B5/055
    • G01R33/56509G01R33/5676G01R33/5608
    • A method whereby motion can be detected in real time during the acquisition of MRI data. This enables the implementation of several algorithms to reduce or eliminate this motion from an image as it is being acquired. The method is an extension of the acceptance/rejection method algorithm called the diminishing variance algorithm (DVA). With this method, a complete set of preliminary data is acquired along with information about the relative motion position of each frame of data. After all the preliminary data is acquired, the position information is used to determine which lines are most corrupted by motion. Frames of data are then reacquired, starting with the most corrupted frame. The position information is continually updated in an iterative process, therefore each subsequent reacquisition is always done on the worst frame of data. The algorithm has been implemented on several different types of sequences, and preliminary in vivo studies indicate that motion artifacts are dramatically reduced.
    • 可以在获取MRI数据期间实时地检测运动的方法。 这使得能够实现几种算法以在图像被获取时减少或消除该运动。 该方法是称为递减方差算法(DVA)的接受/拒绝方法算法的扩展。 利用该方法,获取一组完整的初步数据以及关于每帧数据的相对运动位置的信息。 在获取所有初步数据之后,位置信息用于确定哪些行被运动损坏最多。 然后重新获取数据帧,从最坏的帧开始。 位置信息在迭代过程中不断更新,因此每个后续的重新捕获总是在最差的数据帧上完成。 该算法已经在几种不同类型的序列上实现,并且初步的体内研究表明,运动伪像被大大减少。